A system that compresses air compresses all of the gases and vapors that exist in the air that enter the system. Immediately following the compression function the gases and vapors are still in their gaseous state as a result of the high temperatures from the almost adiabatic compression process. However, due to the subsequent transfer of the heat of compression to the outside air, the temperature of the compressed air in the system rapidly approaches ambient air temperature. Water vapor, one of the constituents of air, undergoes a phase transformation at a temperature between the compression temperature and ambient air temperature. The air in the system becomes saturated with water vapor and liquid water condenses.
Water in the liquid state has a detrimental affect on an air compressor system. Water washes away lubricants and, when the ambient temperature drops below the freezing point, water freezes in the system causing equipment stoppage, possible malfunction and danger.
Desiccant air dryers have been used to remove liquid water and water vapor from compressed air systems. Desiccant materials, however, eventually become saturated and stop absorbing water vapor. Several methods have been employed to regenerate saturated desiccants so that they may be reused. In one method, the system is shut down while water-saturated desiccant is removed and dried by heating. In other systems, two desiccant containers are alternately on-line between the compressor and the pressure reservoir. Each desiccant container is provided with a heating source. The desiccant container which is off-line at any particular time is opened to the atmosphere and heated to drive off the trapped moisture. Refinements of this method use a small amount of the dried outflow from the on-line cylinder to help dry the desiccant in the off-line cylinder.
Although the preceding methods are known to work, they are inconvenient and costly to install and to operate. In addition, they make inadequate provision for disposing of oil particles and burned carbon particles which normally pass from the compressor in the air stream. The oil particles, if not removed, poison the desiccant material.